This invention relates to projection video systems and specifically to a color correction systems for a projection video systems utilizing a single light valve, but multiple sources of illumination.
Most commercially available projection video systems utilize separate projection systems for each of the three primary colors. The systems thus require three light valves with separate optical systems which must be accurately converged on the screen, which adds to complexity and expense. Recently, projection video systems utilizing only a single light valve have been developed. One such system is a color field sequential system, in which the normal video field, 1/60th of a second, is broken into three parts, or color subfields of 1/180th of a second. During the three color subfields, the light valve is illuminated with red, green and blue light sequentially. While the light valve is illuminated with any given color, the video data corresponding to that color is displayed on the light valve. The eye then fuses the three color sub-fields into a single, full color field. The eye also fuses successive video fields and frames into full motion, full color video.
Recently, improved light valves particularly suitable for use in projection television systems have become available. One such device is a so-called deformable mirror device (sometimes called a digital mirror device or DMD) which is illustrated in U.S. Pat. No. 5,079,544 and patents referenced therein, in which the light valve consists of an array of tiny movable mirror-like pixels for deflecting a beam of light either to the display screen (on) or away from the display optics (off). This device is suitable for use in a field sequential system because its pixels are capable of being switched very rapidly. By further rapid switching of the pixels a grey scale is generated.
In addition to improved light valves for use in projection video systems, improved projection lamps are also now available. These projection lamps are highly efficient and have a long life. Furthermore, these lamps are physically quite small and have a small arc length. Small size and small arc length can significantly reduce the size and cost of the optics used to project the light onto the light valve as well as onto the viewing surface. Smaller optics can considerably reduce the overall cost of a video projection system since the optical elements of the system are a very significant portion of the overall cost. Many such lamps are also capable of following an electrical drive signal with good fidelity, i.e. they have a fast rise and fall time and can follow any reasonable waveform, including squarewaves. One such lamp is the Philips CSL-R100W Ultra High Pressure Projection lamp.
However, many otherwise suitable lamps may not have even color distribution across the visible spectrum, i.e. they may be deficient in one or more colors. Furthermore, these lamps have carefully designed thermal properties which require operation at a given power level in order to assure optimal power dissipation. Accordingly, such lamps require a consistent power input over time, such as 100 watts. If greater power is input to the lamp, the lamp will have a significantly shortened life span but turning down the power input to the lamp will cause the lamp to become unstable or go out altogether. The present invention is directed towards providing a three-lamp, single light valve projection video system that can take full advantage of these improved projection lamps while operating the lamps at optimum parameters.
In addition to correcting for any color spectrum deficiencies of the projection lamps used in a projection video system, a suitable video projection system must also provide for color correction of the dichroic filters utilized to convert the white light output from the projection lamps to the primary colors. Dichroic filters are manufactured in a batch process and there are sample to sample variations in the colorimetry of these filters. Additionally upon exposure to the intense light of projection lamps, the colors of the dichroic filters may fade. Accordingly, any suitable projection system must be able to compensate for batch to batch variation and/or fading of the dichroic filters. Finally, a suitable projection video system should also provide for color correction based on user preference, either statically or dynamically.
U.S. patent application Ser. No. 08/141,145 filed Oct. 21, 1993 entitled "Color Correction System for Video Projector", is directed to a method for dynamically color correcting a projection video system utilizing a single projection lamp, a color wheel of dichroic filters and a single light valve. The disclosure of U.S. application Ser. No. 08/141,145 is hereby incorporated by reference, as if fully set forth herein. The present application is directed to a color video projection system utilizing multiple projection lamps and a single light valve.